Is your boot pool “system” or “ssd”? It seems you would want to update the boot codes on the boot pool, not your data pool. The section in the FreeBSD Handbook on upgrading pools has a warning to update the boot code, but does not say how to do it and defers to the gpart man page, which also does not say how to do it. This post confuses me a bit on which pool’s disk you needed to update.